Contamination resisting hat for magnetrons



March I, 1949. u c msb v 2,463,388

CONTAMINATION RESISTING HAT FOR MAGNE'IRONS Filed Jan. 3, 1946 INVENTORFRANKLIN HUTCHINSON' BY Z e/-'M2H4u.

ATTORNEY Patented Mar. 1, 1949 CONTAIHINATION RESISTI'NG HAT FORMAGNETRONS Franklin Hutchinson, New Haven, Conn., as-

signor, by mesne assignments, to the United States of America asrepresented by the Secretary of War Application January 3, 1946, SerialNo. 638,884

3 Claims. 1

My invention relates to thermionic tube apparatus and more particularlyto the emitting members of such tubes.

In thermionic apparatus of the magnetron type, there is provided ananode, an emitting cathode and a shield or hat member positionedadjacent the cathode for the purpose of constricting the path in whichthe electrons from the cathode may travel. In those magnetrons whosecathode hats normally 'attain a temperature of around 700 C. or higher,certain phenomena, usually referred to as leakage, are sometimes notedduring the performance of the tube. These phenomena are believed to bedue in part to the emission of electrons from the hat possibly owing totheir becoming coated in some fashion with oxide coating material fromthe emitting surface of the cathode. Accordingly, it is one of theobjects of my invention to provide a device in which this effect isminimized.

In the prior art to which this invention belongs, attempts have beenmade to prevent emission from the shield or hat by coating the hat withmaterials such as tungsten powder, zirconium and some other materialswhich are supposed to be poor bases for oxide materials used in cathodesand which evaporates from the oathode and deposits on the shield. Thishas not proven altogether satisfactory because, while the device willwork in a desirable fashion for a limited period of time, after a whilenoticeable leakage occurs possibly due to the inequality in expansionbetween the tungsten or zirconium and the nickel base with which it isusually used. Again the zirconium presents diificulties in coating andconsiderable labor is involved in preparing the shield member.Accordingly it is an object of the present invention to provide a moresatisfactory and desirable form of shield or hat arrangement whicheliminates the use of poisoning materials on the hat by making the hatitself of a material which in itself is a poor base for oxides of whichthe cathodes normally are formed.

It is a further object of my invention to provide a shield or hatarrangement for use with the cathode in the magnetron which will behighly satisfactory, simple in nature and easy to manufacture.

It has been found that substantially pure iron having a very thin filmof barium and/or strontium oxide evaporated onto it such as would occurin the operation of a magnetron for instance, has a very poor electronemission characteristic. Therefore by making the hat or shield of thismaterial, the aims and objects of the invention are accomplished.Relative emission characteristics will be described hereinafter withrespect to the description of Fig. 3. My invention will best beunderstood by reference to the drawings in which:

Fig. 1 is a partial top view of a vane type of magnetron showing theprinciple of my invention;

Fig. 2 is a cross-sectional view along line 2-2 of Fig. 1;

Referring to Fig. 1, there is shown a partial top view of a vane type ofmagnetron constructed in accordance with my invention. In this view theposition of a portion of the vanes relative to the cathode isillustrated. The cathode i0 having the hat members II at the endsthereof is located at the center of the apparatus, and the anode members12 are radially disposed thereabout and are spaced at equal distancearound the cathode. It will be appreciated that this is purely anillustrative arrangement and no attempt has been made to show either theproper number or the desirable number of vanes that might be used in themagnetron.

Referring to Fig. 2, there is shown a relative arrangement of thecathode l0 having the hat members [I constructed of Svea iron withrespect to the anode members I2. This is a partial view on a cuttingplane taken along a line of sight 2-2 of Fig. 1. The object of this viewis merely to illustrate the relative position of the upper and loweredges of the vane and the hat members on the cathode. It will further beappreciated that this is for illustrative purposes only and that thearrangement could be equally well applied to the so-called resonantcavity type of magnetron as well as other types.

Sleeves of typical cathode shield material were tested for electronemission under typical conditions met with in service after having beenprepared in a manner also typical of the conditions met with in service.These test sleeves were prepared by being heated and then havingevaporated onto them an amount of electron emitting oxide coatingequivalent to the amount evaporated onto a shield from a cathodeoperating at 850 centigrade for hundreds of hours.

The D.-C. emission from the sleeve at 400 volts plate potential as afunction of temperature was taken over a range of temperatures in whichthe emission was stable. The following emission was noted:

Where the test sleeve was comprised of zirconium powder in anitrocellulose binder and operated on grade A nickel where the sleevehad been heated up to 1000 centigrade and then held at approximately 600centigrade during evaporation of the oxide cathode, the emission of 800Centigrade operating temperature of the sleeve was from 20, to'40milliamperes -per square centimeter with 4(l0'voltsD.-C. potential onthe plate of the tube. The data is not available on its pulsed emissionhaving a pulse length of 1 micro-- second and pulsed 60 cycles persecond at 5 kilovolts anode potential.

Grade A nickel 3 millimeter tubing from Superior Tube Compan (1941)when-comprising a sleeve which has been flashed: at substantially 1000Centigrade and thenheldat substantially 800 Centigrade duringevaporation of the oxide cathode, showed a D.-C. emissionof 5. to 10milliamperes per square centimeter with 400 volts anode potential in thetube and showeda: pulsed emission of .1 amperes per square centimeter at1000 Centigrade operating temperature where the pulses were 1microsecond inlength and the pulse rate was. 60 per second. with. 5kilovolts anode potential.

Sveametal tubes from. .005 inch. sheet metal manufactured by the SwedishIron Corporation of America and. flashed at substantially 1000Centigrade and then held at substantially 600? Centigrade duringevaporation of the oxide cath? ode showed zero emission at-800 operatingtemperature and 400 volts D.-C. potential on the anode of the tube. Itspulsed-emission under thesame conditions as the grade A. nickel was toolow to observe.

While the preferred embodiment of this invention has been set forthhereinbefore, it will be appreciated that there may be deviationstherefrom which will fall within the spirit of the invention andaccordingly I claim such deviations which. fall fairly withinthespiritand scope of the hereinafter appended claims.

What is claimed is:

1. A magnetron cathode having no end leakage comprising a cylindricalcathode having an electron emitting coating on its cylindrical surfaceand shields enclosing the ends of said cylindrical cathode, the saidshields being made of iron.

2; A magnetron. cathode having no end leakage comprisinga cylindricalcathode with a cylindrical electron emitting surface and shield hatsmade of iron enclosing the ends of said cathode.

3-. A cathode for a high frequency thermionic tube having no end leakagecomprising a cathode having electron emitting. longitudinal surfaces andendsurfaces, and shield.hats made-ofiron fitted over said end surfaces;

FRANKLIN HUTCHINSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date.-

1,886,705 Lucian Nov. 8;. 1932' 2,208,406 Benedict July 16, 19402,418,117 Hale-ct a1 Apr. 1, 1947-

